Six studies from across the world found high occupancy rates for artificial burrows by seabirds, with three finding that occupancy increased over time, taking years to build up. Three studies from across the world found very low occupancy rates for artificial burrows used by petrel species.

Eight studies from across the world found that the productivity of birds using artificial burrows was high, in many cases as high or higher than in natural burrows. One replicated study from the USA and a small study from the Galapagos found low productivity of petrels using artificial burrows.

Background information and definitions

Many petrels and shearwaters and auks nest underground in burrows dug themselves or burrowing mammals such as rabbits. This means that they require very different artificial nests to the ground- and tree-nesting species discussed in the previous section.

Supporting evidence from individual studies

1

A replicated and controlled study in 1980-84 on an island in Washington State, USA (Wilson 1986), found that rhinoceros auklet Cerorhinca monocerata nesting success was at least as high for individuals nesting in artificial burrows as it was for those in natural burrows (50-89% of 10-20 artificial burrows producing chicks vs. an estimated 53-56% success for natural burrows). No differences in growth rates of chicks in artificial and natural burrows were detected. Burrows were plywood chambers (23 × 25 × 71 cm) with a 91 cm long, 13-15 cm diameter entrance tunnel. Chambers were buried 15 cm underground after being filled with fresh soil and arranged so entrances faced the sea.

2

A replicated trial in 1980-3 on four islands in Maine, USA (Podolsky & Kress 1989), found that only two Leach’s storm petrel Oceanodroma leucorhoa chicks fledged successfully from 264 artificial burrows over three years (both in the third year). Between 14 and 46 burrows (5-17%) were colonised, with 6-10 being used for breeding. A total of 22 eggs were produced over three years, of which ten hatched, producing two chicks. Burrows had a 40-50 cm entrance tunnel (10 cm diameter) and a 25 x 25 x 25 cm nest chamber set to one side and covered with a large flat rock (for inspection). This study also describes the impact of playing vocalisations to attract petrels, described in (‘Use vocalisations to attract birds to safe areas’).

3

A replicated trial on an island in Washington State, USA, in 1989-91 (Wilson 1993), found that rhinoceros auklets Cerorhinca monocerata used an average of 91% of 40 artificial burrows provided, with 58% of burrows (64% of occupied burrows) producing chicks. There were no differences in use or productivity between burrows in areas occupied by glaucous-winged gulls Larus glaucescens and those without gulls. Artificial burrows were of the same design as in Wilson 1986, with 20 spread over approximately 300 m of cliff.

4

A replicated controlled trial in 1992-4 on Cabbage Tree Island, New South Wales, Australia (Priddel & Carlile 1995), found that Gould’s petrel Pterofroma leucoptera leucoptera breeding success was comparable or higher in artificial burrows, compared to natural cavities (36-63% breeding success for 14-19 pairs in artificial burrows vs. 23-31% success for natural cavities in previous years). The number of birds using artificial burrows increased over time, from 53% of 90 boxes visited but no eggs laid in 1992 to 19 eggs laid, and 13 chicks fledging in 1994. Burrows consisted of a 20 × 25 × 52 cm polyethylene box, accessed through a 40 cm long tunnel of 10 cm diameter PVC piping. In 1993, many eggs rolled into the entrance tunnel, so a 4 cm barrier was added at the nest chamber entrance in 1994.

5

A controlled, replicated study 1993-4 on Mousa, Shetland, northern Scotland (Bolton 1996), found that hatching and fledging rates of European storm petrels Hydrobates pelagicus in artificial nests was not significantly different from those in natural nests (93% of 29 eggs in artificial nests hatched and 81% of 27 nestlings fledged vs. 81% of 42 eggs and 62% of 34 chicks in natural nests). Overall, 36% of 81 boxes were used each year, with 26 nests on a boulder beach used more often than 55 nests in dry stone walls (46% vs. 31-33% respectively). Nests had a nesting chamber of 10 cm long, 15.2 cm diameter PVC piping, an observation chamber and a 6 cm diameter entrance tunnel.

6

A replicated study on Santa Cruz in the Galápagos Islands, Ecuador (Cruz & Cruz 1996), found that the use of artificial burrows by dark-rumped petrels Pterodroma phaeopygia phaeopygia increased each year from 1988-90, although only one chick was fledged from the burrows. In 1988, 68% of the eighty burrows were prospected by petrels, although none nested. In 1989, 39 petrels staying in burrows overnight and in 1990, four pairs laid eggs in burrows. However, three of the four chicks produced were predated, probably by rats. Petrel vocalisations were played at the nest site each night, with the results discussed in ‘Use vocalisations to attract birds to safe areas’. Predator control on the Galápagos Islands is discussed in ‘Control mammalian predators on islands’.

7

A replicated study in 1986-95 on an island in British Columbia, Canada (Gaston 1996), found that ancient murrelets Synthliboramphus antiquus used artificial nest boxes installed in May 1986, but that it took several years for them to regularly use them (7-14% of 26 nest boxes occupied in 1987-9, with eggs laid in only a single burrow each year vs. 67% of 21 boxes occupied in 1995, at least seven rearing young). Nest boxes were 40 x 40 x 13 cm and buried 100-150 m from the sea, within an area used by approximately 5,000 ancient murrelets

8

A replicated study from February-April in 1999 in 21 Chatham petrel Pterodroma axillaris nest sites in the Chatham archipelago, New Zealand (Sullivan et al. 2000), found that artificial nest sites were used by petrels. No details are provided on productivity.

9

A replicated, controlled study on Cabbage Tree Island, New South Wales, Australia, in 1995 (Priddel & Carlile 2001), found that the fledging rate of 30 Gould’s petrel Pterodroma leucoptera chicks translocated from their burrows to artificial nests nearby and hand-fed was not significantly different from control (unmoved, parent-fed) birds (100% of translocated chicks fledging vs. 29/30 controls). Nest burrows were of the type described in (4). This study is also described in ‘Provide supplementary food to increase reproductive success’’, ‘Translocate individuals’ and ‘Artificially incubate and hand-rear birds in captivity’.

10

A controlled before-and-after study in 1997-2001 in two sea caves near Benidorm, Spain (de Leon & Minguez 2003), found that European storm petrels Hydrobates pelagicus nesting in artificial nest boxes had significantly higher nesting success than petrels in natural nests, except in the year boxes were provided (36-49% for 803 natural nests vs. 40-75% for 72 occupied nest boxes). Occupancy rates increased over time (6% of 86 boxes in 1997 to 29% of 83 in 2001) and were higher in a cave not illuminated at night by city lights and for boxes placed over old nest sites. There was no decrease in the number of petrels at natural nesting sites over the study, so the birds in nest boxes probably represented new breeders. Nest boxes were 25 x 12 cm PVC boxes with drainage holes, lined with sand and fitted with a small tunnel preventing access by gulls.

11

A controlled study in 2000-1 on Praia Islet in the Azores, Portugal (Bolton et al. 2004), found that Maderian storm petrels Oceanodroma castro nesting in artificial nest chambers had higher overall productivity than those in natural burrows in two out of three breeding seasons (0.42-0.64 chicks/pair for birds in artificial nests vs. 0.15-0.29 chicks/pair for natural burrows). Between 40 and 49 of 115-147 chambers were used and the authors argue that most birds using them were new breeders, meaning that the early-breeding population and late-breeding populations would have increased by 28% over two years and 11% in one year respectively. Chambers consisted of drainable plastic plant pots lined with stones, soil and dry grass, buried, covered with flexible lids and led to by 6 cm entrance. The pot had holes to ensure water drained through it. This study also used recorded petrel vocalisations to attract petrels to the site, discussed in ‘Use vocalisations to attract birds to safe areas’.

12

A replicated study on Mana Island, North Island, New Zealand (Miskelly & Taylor 2004), found that 49% of 239 common diving petrels Pelecanoides urinatrix fledged successfully after being translocated to the island in 1997-9 from two other islands and hand-reared in artificial nests. However, 94% of 53 breeding attempts on the island until 2003 were in natural burrows, rather than artificial nests. The nests consisted of two buried chambers (30 x 15 cm and 20 x 20 cm) reached by a 60 cm section of 10 cm diameter PVC pipe. This study is discussed in more detail in ‘Artificially incubate and hand-rear birds in captivity’, ‘Use vocalisations to attract birds to safe areas’ and ‘Translocate individuals’.

13

A replicated study on Boondelbah Island, New South Wales, Australia (Priddel et al. 2006), found that 98% of Gould’s petrel Pterodroma leucoptera leucoptera chicks fledged successfully from artificial nests, after being translocated from Cabbage Tree Island, 1.4 km away, leading to the establishment of a new breeding colony. One hundred plastic boxes of the type described in Priddel & Carlile 1995 were installed over a 150 m2 and chicks placed directly in them and supplied with food. This study is discussed in more detail in ‘Translocate individuals’.

14

A before-and-after study on Praia Islet (12 ha), off Graciosa, Azores, Portugal (Bried et al. 2009), found that the breeding population of storm petrel Oceanodroma castro increased from no breeding pairs to almost 800 (before 2000 and in 2006, respectively), following the installation of artificial nesting burrows in 2000. Burrows consisted of a plastic plant pot (with drainage holes), buried and with a 6 cm entrance burrow leading to a hole in the side. Rabbits were also eradicated from the island (see ‘Control or remove habitat-altering mammals’ and habitat restored ‘Shrubland restoration’). The effect of nest boxes for ground-nesting seabirds is also discussed.

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